Shower cold pressure too low

[aharrisreid]

Hi,

I have a mixer-shower fed via. a double-impeller pump receiving hot water from a cylinder (open-vented) and cold water from a feeder tank which also feeds the cylinder. The pump is level with the bottom of the cylinder, about 3m below the feeder tank. The pump was installed because the shower head is only 1m. below the feeder tank.

Now the problem. When the mixer is set to max. cold, the water is medium-hot (just bearable for a shower). When set to max. hot, the water is scalding - far to hot for anyone to stand under.

First I thought cold water was not being drawn through the pump, but the above suggests to me that cold water is reaching the shower, just not enough of it :-(

My next test was to block the hot feed to the pump, then turn on the shower. The pump did not activate, suggesting the cold pressure was not enough to activate the pump, but how come the hot pressure is enough to activate the pump, when they originate from the same tank? Is it possible the microswitch on the cold side is not working properly (I assume it expects roughly the same pressure as the hot side to activate the pump).

I have considered using a pressure-equalising-valve, but as the cold pressure is so low, the hot pressure would become unacceptable. Could I use cold feed from the mains instead, and pass it through a PEV before it reaches the pump? For the record, the pump is a Newteam Duraspeed.

Any ideas would be appreciated.

Alan

 

[WHPES]

NEVER use cold feed from the mains - the hot and cold need to come from the same source. Your problem suggests there is an obstruction somewhere.

Is there a gate valve in the cold feed which could be stuck? Check the cold outlet of the cistern for obstructions.

 

[Plumbstar Tom]

the float switch in the pump will activate both sides so i would check for bloackages as per above, check the filters on the shower and the NRVs. Even try the shower connected without the pump, and then without the pup and the shower off the wall so you just have the supply pipes

 

[aharrisreid]

Thanks to all who replied so far. I'll try your suggestions and let you know how I get on.

Regards,
Alan

 

[aharrisreid]

I have now disconnected the hot and cold feeds to the pump and checked the filters - they were crystal clear! I turned on the cold via. the isolator valve and water shot out at a good pressure, so I can't work-out why the pump is drawing such a small amount of cold compared to the hot.

Any ideas what I should try next?

TIA,
Alan

 

[kay-jay]

if your hot is pumped and the cold is from a header and not pumped then your supplies are not balanced.

both h and c need to be either gravity or pumped which is what we mean by balanced

 

[SimonG]

Is it a thermostatic mixer? If so have you commissioned it? If it's thermostatic you can adjust the min and max temperatures, there should have been instructions with it to do this. I've had the odd shower where I have had to set the temperature manually as the factory presets have been all over the place.

 

[Plumbstar Tom]

if no instructions pull the temp handle off and turn the spindle down and replace the temp handle and try the temperature range then

 

[Plumbstar Tom]

Also the shower has filters so may need to check them on the inlets too

 

[andyplumber]

how is the cold feed being fed to the pump? has it got its own feed from the header tank or does it tee off the cold feed to the cylinder?

 

[aharrisreid]

if your hot is pumped and the cold is from a header and not pumped then your supplies are not balanced.

both h and c need to be either gravity or pumped which is what we mean by balanced

Thanks for that kay-jay - that's something new I've learned today!

Alan

 

[aharrisreid]

Hi Simon
No, it is not a thermostatic mixer. I inherited it from the previous owner and unfortunately there are no instructions.

Regards,
Alan

 

[aharrisreid]

how is the cold feed being fed to the pump? has it got its own feed from the header tank or does it tee off the cold feed to the cylinder?

Hi Andy,
Cold feed to the pump is a tee-off from the cold-feed to the cylinder.

Regards,
Alan

 

[secret squirrel]

If its not a thermostatic mixer this is a big part of the problem, you have to set the temperature manually by using the lever (manual vavle) if its thermostatic the cartridge will do its best to adjust the temperature for you.

You should have a cold feed from the tank dedicated to the cold of the shower.

My advice, bin it start again, you may even be able to speak to the manufacturer of the shower and put a cartridge in.

 

[Nat]

Hi Andy,
Cold feed to the pump is a tee-off from the cold-feed to the cylinder.

Regards,
Alan

The cold should be dedicated. By that I mean run directly from the cwsc to the pump, then to the shower. Not sure if that is what is causing your problem in this instance though.